The objective of undertaking this project is to develop a system, employing the technique of reverse plaque assay that could be used to study spontaneous and induced mutations in mammals using readily available single cells; namely, red blood cells. Antibodies against some of the mouse hemoglobin variants have been raised. A unique plaque assay for mouse red blood cells has been developed using these antibodies. Potential use of the RBC plaque assay for detection of mutation in mouse hemoglobins was studied. Using extensively absorbed goat anti-DBA/2 Hb antibody, as low as 4 DBA/2 RBC could be detected in the presence of a large number of C57BL/6 RBC.